The present invention relates to composite structures. More particularly, the present invention relates to repairing composite structures having a perforated skin and a honeycomb core.
Composite structures are commonly known and used in, for example, gas turbine engines for aerodynamic fairings. One type of composite is a sandwich structure having a face skin, a back skin, and a honeycomb core inserted between and bonded to the face skin and the back skin. The face skin and the back skin may be laminated structures with a resin matrix, such as epoxy, and one or more plies of fiberglass. The face skin commonly includes holes or perforations that extend through a thickness of the face skin to the honeycomb.
The honeycomb may become damaged over time from an impact, elevated temperatures, abrasion, erosion, and/or other factors. In some instances, the honeycomb may be damaged even though there is no damage to the face skin. In some instances, it may be desirable to locally replace a section of honeycomb from the back skin side, rather than replace the entire composite structure. For example, a section of the original honeycomb and a corresponding section of the back skin may be cut out of the composite, and a replacement honeycomb and a replacement back skin may be attached to the face skin.
In a composite having a sandwich structure, ends of the original honeycomb press into the back skin and the face skin to form a dimpled imprint surface on the skins. The dimpled imprint results in each skin having compressed and uncompressed sections, which remain after the original honeycomb is removed. This uneven surface on the face skin makes it difficult to bond a replacement section of honeycomb to the face skin. Thus, it may be necessary to remove some of the face skin to create a more even bonding surface, before attaching the replacement honeycomb to the face skin.
Fiberglass leveling plies and adhesive may be attached to the prepared bonding surface of the face skin, prior to bonding the replacement section of honeycomb to the face skin. During a curing cycle, the perforations of the face skin commonly become blocked with adhesive, resin or fiberglass. Reforming the perforations is time consuming and may structurally damage or weaken the restored composite after curing is complete. There is a need for a method of maintaining the perforations in the face skin during a local repair of the honeycomb and the back skin of the composite.